The present invention relates to a plasma deposition apparatus into which raw material gases are introduced to deposit various kinds of material on a specimen substrate by using plasma reaction so as to form a thin film of Si, Si.sub.3 N.sub.4, SiO.sub.2, MoSi.sub.2, WSi.sub.2 or the like and which is utilized to manufacture various electronic devices such as semiconductor integrated circuits.
As an apparatus for forming a thin film, CVD (Chemical Vapor Deposition) apparatus is known and is of particular used frequently as means for forming various thin films in a semiconductor integrated circuit, the CVD apparatus can form thin films such as Si.sub.3 N.sub.4, SiO.sub.2, Si or the like with a high purity and a high quality. In the reaction process of forming a thin film, a reaction vessel in which specimen substrates are arranged is heated at a high temperature condition of 500.degree.-1,000.degree. C. Raw material to be deposited is supplied to the vessel in the form of gaseous composition, so that gaseous molecules are thermally dissociated and combined in the gas and on the surface of the specimen so as to form a thin film.
This method, however, utilizes the thermal reaction in the high temperature condition, and accordingly the kinds of specimen substrates on which a thin film is to be deposited are limited to substrates which have a heat resistance against the high temperature and characteristics which are not deteriorated by the high temperature. Therefore, there is a disadvantage in that an area to which the CVD apparatus is applied is extremely restricted. In addition, there is also another disadvantage in that it is difficult to control characteristics of the formed film such as internal stress.
Recently, in order to solve these disadvantages, a plasma-enhanced CVD apparatus has been developed in which the plasma reaction is utilized to perform a reaction similar to that of CVD apparatus at a relatively low temperature to form a thin film. The plasma-enhanced CVD apparatus was explained, for instance, by Richard S. Rosler et al. in "A Production Reactor for Low Temperature Plasma-Enhanced Silicon Nitride Deposition", SOLID STATE TECHNOLOGY/June 1976, pp. 45-50. A. K. Sinha et al. also disclosed the plasma-enhanced CVD in "Reactive Plasma Deposited Si--N Films for MOS-LSI Passivation", J. Electrochem. Soc.: SOLID-STATE SCIENCE AND TECHNOLOGY, April 1978, pp. 601-608. This plasma CVD apparatus is comprised of a specimen chamber, a gas introducing system and an exhausting system. There are arranged inside of the specimen chamber a radio frequency electrode and a specimen table which are opposite to each other. This specimen table has a heating mechanism. Explanation will be made with respect to one example of forming a silicon nitride film. Silane gas (SiH.sub.4) and ammonia gas (NH.sub.3) are introduced as raw material into the specimen chamber from the gas introducing system. While these raw material gases are exhausted from the exhausting system, the gaseous pressure in the specimen chamber is kept constant within a range from 0.1 to 10 Torr. Radio frequency power is supplied to the specimen chamber to produce plasma. The gaseous molecules of SiH.sub.4 and NH.sub.3 are dissociated in the plasma. Subjected to the incidence of ions and electrons besides the dissociation in the plasma, silicon nitride is deposited on a surface of a specimen substrate on the specimen table. In this case, however, the specimen table is heated at 300.degree.-500.degree. C. and also it is necessary to additionally use a thermal reaction in a high temperature condition. Accordingly, the plasma-enhanced CVD apparatus is still insufficient for the purpose of the formation of thin film while the specimen substrate is kept at a low temperature. In addition, the dissociation of SiH.sub.4 and NH.sub.3 are not sufficient, so that H is incorporated in a formed film or the Si--N bond is not sufficient. As a result, a thin film is not obtained with a high quality. It follows that there is a disadvantage in that the plasma-enhanced CVD apparatus is not applicable to the fabrication of such semiconductor integrated circuits that require a specimen substrate with a low heat resistance and a film with a high quality.
On the other hand, as another method for utilizing the plasma, a method called the plasma stream transport method is known. This method was, for instance explained by Takashi Tsuchimoto in "Plasma stream transport method (1) Fundamental concept and experiment", J. Vac. Sci. Technol. 15(1), January/February 1978, pp. 70-73, and "Plasma stream transport method (2) Use of charge exchange plasma source", J. Vac. Sci. Technol. 15(5), September/October 1978, pp. 1730-1733. These papers describe the studies on the formation and control of the plasma stream for transporting material. This method is applied to both formation of a thin film and etching. The device for this method is composed of a plasma source, which utilizes the microwave discharge, and a specimen chamber provided with the parallel magnetic field. By using the magnetic pipe effect of the parallel magnetic field, the plasma stream is transported to a surface of a specimen from the plasma source through thermal diffusion, thereby depositing a film on the specimen. However, when applying this method to film formation, the plasma stream is merely transported through thermal diffusion, while the effects of incidence and impingement of ions, electrons, etc. on the film-forming reaction on the specimen surface are scarcely used. Accordingly, also in the plasma stream transport method, it was necessary to heat the specimen at a temperature of 300.degree.-500.degree. C. so as to use a thermal reaction through the heat energy at the same time. In addition, the plasma source used in the plasma stream transport method utilizes the microwave discharge with a discharge chamber of coaxial construction or the microwave discharge in a wave guide cylinder. Accordingly, the diameter of the plasma stream is as small as about 2 cm and, thus, the area where a film can be formed is small. This results in the disadvantage in that the productivity is considerably low. Moreover, with this method, it is necessary to lower the gas pressure in the specimen chamber so as not to attenuate the density of the plasma which reaches the specimen surface. It is further necessary to set the inside of the plasma source to a gas pressure which is suitable for discharge. For this reason, the diameter of the orifice to introduce the plasma cannot be increased and, consequently, it is difficult to increase the diameter of the plasma stream.
On the other hand, it was attempted to scan the plasma stream by using a magnetic coil for scanning in order to increase the area where a film can be formed. With this method, however, the film forming speed reduces accordingly and productivity is not improved. This method also requires a complicated composition. Moreover, when it is for example intended to introduce N.sub.2 gas to the plasma source and to introduce SiH.sub.4 gas into the specimen chamber to form a silicon nitride film for the purpose of avoiding dissipation of raw material gases or formation of detrimental deposits inside the plasma source, there is a disadvantage in that the interaction between the N.sub.2 plasma stream and SiH.sub.4 gas is insufficient so that a film of a high quality cannot be formed with a high efficiency. This is because the diameter of the plasma stream is small and, in addition, the gas pressure of SiH.sub.4 in the specimen chamber cannot be increased.